The present invention relates to a method of generating compressed air, particularly for commercial vehicles. The compressed air is generated from ambient air by way of a compressor unit driven via an internal-combustion engine in accordance with a control unit. In addition, the invention relates to a compressor arrangement for implementing the method.
In the field of commercial vehicles, which is of special interest here, such methods and compressor arrangements, respectively, are used for carrying out the compressed-air procurement of the on-board pneumatic system of a commercial vehicle. The pneumatic system on board a commercial vehicle is required, in particular, for supplying the brake system, the pneumatic suspension, the trailer and diverse secondary consuming devices. The compressor arrangement of a commercial vehicle generates compressed air of up to 12.5 bar for this purpose.
The product information “High-Performance Compressors” of the firm KNORR-BREMSE Systeme für Nutzfahrzeuge GmbH (Printing No. P-3505-DE-01) discloses a compressor unit, which is constructed in the form of a piston compressor. A crankshaft rotatingly disposed in a compressor housing converts an input-side rotating movement, by means of the crankshaft drive principle, to a linear back and forth movement of an assigned piston housed in a cylinder. The piston, interacting with a valve device housed in the cylinder cover, takes in the ambient air and subsequently delivers it in a compressed state. The compressor unit is available in one-cylinder or two-cylinder designs. The one-cylinder design, at a maximum rpm of 3,000 revolutions per minute, has a delivery capacity of approximately 550 l/min. In contrast, the two-cylinder design is provided for pneumatic systems with a relatively high compressed-air consumption and, correspondingly, also has a higher delivery capacity; here, at a maximal rotational speed of 3,000 revolutions per minute, a delivery capacity of approximately 1,200 l/min.
The drive of the compressor unit takes place in a generally known manner by way of the internal-combustion engine of the commercial vehicle. In some application cases, a rotational-speed-transmitting transmission unit is connected between the internal-combustion engine and the compressor unit. In this case, the transmission unit of the compressor unit is usually integrated directly in the vehicle transmission of the commercial vehicle.
Such compressor arrangements of the prior art are, in addition, equipped with technical measures for saving energy. Thus, the operation of the above-described known compressor arrangement takes place by way of a control, which starts the operation of the compressor unit only when a compressed-air demand exists in the pneumatic system of the commercial vehicle. In most cases, the compressed-air demand is determined by way of a pressure sensor connected with the system pressure. If the system pressure falls below a defined threshold pressure, then the operation of the compressor unit is started, in order to again build up a sufficient air pressure. For storing the built-up pressure, in the case of the compressed-air system, normally one or more pressure reservoirs are used, which reservoirs have as large a volume as possible.
A demand control for the operation of the known compressor unit takes place by a switching of the compressor unit between a delivery phase and an idling phase. In the delivery phase, compressed air is generated from the ambient air and the pneumatic system is fed. In contrast, in the idling phase, the compressor unit runs without a load, so that, although a piston movement takes place, no compressed air reaches the pneumatic system. This compressed air will then be discharged to the outside. Since, because of the absent load, in the idling phase (in contrast to the delivery phase), much less power is consumed by the compressor unit, this type of air demand control contributes to the saving of energy.
However, it is disadvantageous that, in the delivery phase, the compressor unit has to work predominantly against a pressure of from 10 to 12.5 bar. Particularly, in the case of a one-stage compressor unit, this high counterpressure causes a high power consumption. In contrast, the compressed-air consuming devices of the pneumatic system require different amounts of operating pressure. Thus, for example, the operation of the brake system requires an air pressure of from 10 to 12 bar; the pneumatic suspension requires approximately 12 bar; and the trailer of a commercial vehicle operates with an air pressure of 8.5 bar. So far, these different operating pressures, starting from the maximal pressure of approximately 12.5 bar—generated by the compressor unit—were reduced by the control unit—for example, in the form of an APU (Air Processing Unit) or an EAC (Electronic Air Control). However, with respect to the energy required for operation, this method proves to be quite ineffective in practice.
It is therefore an object of the present invention to further improve a method, as well as a compressor arrangement, of the above-mentioned type such that a lower energy consumption is required for generating the compressed air.
With respect to the method, this object is achieved by a method of generating compressed air, particularly for commercial vehicles, which compressed air is generated from ambient air by way of a compressor unit driven by an internal-combustion engine according to a control unit. The compressor unit, operated by the internal-combustion engine, generates compressed air of only a low pressure level for assigned low-pressure consuming device. Starting from the compressed air of the low pressure level, via a separate auxiliary compressor unit, compressed air of a higher pressure level for assigned high-pressure consuming devices is generated. The coordinated triggering of the two compressor units is carried out, controlled by the pressure demand, centrally through the use of the control unit.
With respect to a compressor arrangement for implementing the method, the object is achieved by a compressor arrangement, particularly for commercial vehicles, having an internal-combustion engine for generating a rotating movement, which drives an output-side compressor unit for generating compressed air from the ambient air. The control unit triggers the compressed-air generation when compressed air is required. The compressor unit, operated by the internal-combustion engine, generates compressed air of only a low pressure level for assigned low-pressure consuming devices. Starting from the compressed air of this low pressure level, a separate auxiliary compressor unit generates compressed air of a higher pressure level for assigned high-pressure consuming devices. The control unit is provided for the coordinated, pressure-demand-controlled triggering of the two compressor units. Other advantageous further developments of the invention are described and claimed herein.
The invention includes the technical teaching that, by means of the combustion-engine-operated conventional compressor unit, only compressed air of a low pressure level is generated for assigned low-pressure consuming devices, whereas, based on this compressed air of the low pressure level, by means of a separate auxiliary compressor unit, compressed air of a higher pressure level for assigned high-pressure consuming devices is generated, in which case the coordinated triggering of both compressor units is carried out, controlled by the pressure demand, centrally through use of the control unit.
The advantages of the invention are achieved, in particular, from the fact that the conventional combustion-engine-operated compressor unit only still works against an air pressure of maximally 8.5 bar, whereby the compressor unit can be operated more effectively with a lower energy consumption. For the comparatively higher pressure level, which is required by the high-pressure consuming devices of the compressed-air system, a separate auxiliary compressor unit is used. This auxiliary compressor unit is completely separated from the internal-combustion-engine-operated compressor unit. With respect to the energy balance, the largest fraction of energy is still required by the compressor unit operated by the internal-combustion engine; but the higher pressure level is generated by the auxiliary compressor unit, which can be operated more effectively in this range. In comparison to the compressor unit operated by the internal-combustion engine, the separate auxiliary compressor unit of the higher pressure level needs to be operated only with a shorter switch-on duration in order to cover the occurring high-pressure requirement. On the whole, this results in a considerable savings of energy. For controlling the two compressor units in a coordinated manner, a joint control unit is provided. The joint control unit triggers the corresponding compressor unit in the case of a compressed-air demand in the low pressure level or a compressed-air demand in the higher pressure level.
According to a preferred embodiment, the compressed air of the low pressure level is stored in an assigned low-pressure reservoir, and the compressed air of the high pressure level is stored in an assigned high-pressure reservoir. In the high-pressure reservoir, also up to 20 bar—generated by the auxiliary compressor unit—can be stored so that, while the reservoir volume is the same, approximately twice the amount of energy can be stored. This maximal pressure level can be adapted corresponding to the operating pressure of the compressed-air consuming devices; that is, it can be reduced.
Furthermore, it is contemplated that the auxiliary compressor unit can be used for implementing an emergency function, which consists of covering the compressed-air demand at least temporarily by means of the auxiliary compressor unit in the event of the failure of the compressor unit operated by the internal-combustion engine. Correspondingly, the separate auxiliary compressor unit should not be driven by the internal-combustion engine of the commercial vehicle but, rather, by a redundant drive unit. A suitable drive unit is, for example, an electric motor which is provided with sufficient power by way of the electrical wiring of the commercial vehicle.
The control unit of the commercial vehicle used for triggering both compressor units controls the separate auxiliary compressor unit preferably indirectly by switching the input-side electric motor on and off. For the rotational speed adaptation, it is contemplated to arrange a suitable transmission between the electric motor and the auxiliary compressor unit. The auxiliary compressor unit, together with the electric motor and, optionally, with the transmission unit preferably forms a single system module. The single system module can be detachably mounted at the appropriate point on the commercial vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.